Real-time reactor coolant system boron concentration monitor utilizing an ultrasonic spectroscpopy system

ABSTRACT

A method and a system for performing real-time, continuous, measurements of the boron concentration in the water entering a nuclear reactor coolant system. The invention utilizes knowledge of the impact that boron contained in liquid water has on the attenuation of acoustic or ultrasonic waves. This information, coupled with radiation damage resistant and high temperature operability capable transmitter and receiver equipment, provides the means to place the measurement system sensors and signal processing electronics on the reactor coolant system charging flow piping or the hot leg or cold leg of the reactor coolant loop. This will allow the reactor operator to directly monitor both the reactor coolant system boron concentration value and detect changes in the reactor coolant system boron concentration relative to a reference value as they occur.

BACKGROUND

1. Field

This invention relates in general to light water nuclear reactors and inparticular to an instrumentation system for monitoring in real time theboron concentration within the reactor coolant.

2. Related Art

The primary side of nuclear reactor power generating systems which arecooled with water under pressure comprises a closed circuit which isisolated and in heat exchange relationship with the secondary side forthe production of useful energy. The primary side comprises the reactorvessel enclosing a core internal structure that supports a plurality offuel assemblies containing fissile material, the primary circuit withinheat exchange steam generators, the inner volume of a pressurizer, pumpsand pipes for circulating pressurized water; the pipes connecting eachof the steam generators and pumps to the reactor vessel independently.Each of the parts of the primary side comprising a steam generator, apump and a system of pipes which are connected to the vessel form a loopof the primary side.

For the purpose of illustration, FIG. 1 shows a simplified nuclearreactor primary system, including a generally cylindrical reactorpressure vessel 10 having a closure head 12 (also shown in FIG. 2),enclosing a nuclear core 14. A liquid reactor coolant, such as water ispumped into the vessel 10 by pump 16 through the core 14 where heatenergy is absorbed and is discharged to a heat exchanger 18, typicallyreferred to as a steam generator in which heat is transferred to autilization circuit (not shown), such as a steam driven turbinegenerator. The reactor coolant is then returned to the pump 16,completing the primary loop. Typically, a plurality of the abovedescribed loops are connected to a single reactor vessel 10 by reactorcoolant piping 20. At least one of those loops normally includes apressurizer 19 connected to the reactor coolant loop piping 20 through acharging line 21.

An exemplary reactor design is shown in more detail in FIG. 2. Inaddition to the core 14 comprised of a plurality of parallel, vertical,co-extending fuel assemblies 22, for purposes of this description, theother vessel internal structure can be divided into the lower internals24 and the upper internals 26. In conventional designs, the lowerinternals' function is to support, align and guide core components andinstrumentation as well as direct flow within the vessel. The upperinternals restrain or provide a secondary restraint for the fuelassemblies 22 (only two of which are shown for simplicity in thisfigure), and support and guide instrumentation and components, such ascontrol rods 28. In the exemplary reactor shown in FIG. 2, coolantenters the reactor vessel 10 through one or more inlet nozzles 30, flowsdown through an annulus between the vessel and the core barrel 32, isturned 180 degrees in a lower plenum 34, passes upwardly through a lowersupport plate 37 and a lower core plate 36 upon which the fuelassemblies 22 are seated and through and about the assemblies. In somedesigns, the lower support plate 37 and the lower core plate 36 arereplaced by a single structure, the lower core support plate, at thesame elevation as the lower support plate 37. The coolant flowingthrough the core 14 and surrounding area 38 is typically large on theorder of 400,000 gallons per minute at a velocity of approximately 20feet per second. The resulting pressure drop and frictional forces tendto cause the fuel assemblies to rise, which movement is restrained bythe upper internals 26, including a circular upper core plate 40.Coolant exiting core 14 flows along the underside of the upper coreplate 40 and upwardly through a plurality of perforations 42. Thecoolant then flows upwardly and radially to one or more outlet nozzles44.

The upper internals 26 can be supported from the vessel 10 or the vesselhead 12 and include an upper support assembly 46. Loads are transmittedbetween the upper support assembly 46 and the upper core plate 40,primarily by a plurality of support columns 48. A support column isaligned above a selected fuel assembly 22 and perforations 42 in theupper core plates 40.

The rectilinearly movable control rods 28 typically include a drive rod50 and a spider assembly 52 of neutron poison rods 28 that are guidedthrough the upper internals 26 and into aligned fuel assemblies 22 bycontrol rod guide tubes 54. The guide tubes are fixedly joined to theupper support assembly 46 and connected to the top of the upper coreplate 40. By inserting and withdrawing the neutron poison rods into andout of guide thimbles within the fuel assemblies within the core thecontrol rods regulate the extent of the nuclear reactions within thecore. Boron, dissolved within the reactor coolant water, also functionsto control the nuclear reactions and manages more gradual changes inreactivity than the control rods.

There is currently no direct method employed to continuously measure theboron concentration in the reactor coolant system. Current measurementsrely on samples drawn from taps in the reactor coolant system that havepiping running from inside the Reactor Containment Building to ChemistryAnalysis Offices located in the Auxiliary Building. This methodologyresults in a significant time lag between the boron concentrationmeasured in the sample drawn and the current reactor coolant systemboron concentration during reactor coolant system boron concentrationdilution and boration transient conditions. This necessitates monitoringfor uncontrolled changes in reactor coolant system boron via changes inreactor reactivity using changes in reactor neutron flux levels. Thisapproach is not typically capable of detecting core reactivity changesuntil significant reactivity changes have already occurred. Thissituation has resulted in many adverse “Reactivity Management” OperatingEvent incidents associated with inadvertent changes in reactor coolantsystem boron concentration resulting in uncontrolled core reactivitychanges.

It is also necessary to monitor the reactor coolant system boronconcentration to ensure that reactor Shutdown Margin is maintained whenthe reactor is shutdown. Boron concentration values are required duringoperation to ensure that the reactor is behaving in agreement withdesign expectations. Managing reactor coolant system boron concentrationchanges to compensate for fuel depletion during operation also requiresdetailed information on the value and changes in reactor coolant systemboron concentration. Reactor coolant system boron dilution is requireddaily to compensate for fuel depletion. Ensuring that the desiredreactor coolant system boron concentration change is occurring or hasoccurred is affected by the time lag caused by the current reactorcoolant system boron concentration measurement process. Mistakes in therequired amount of dilution required are only detected after they havealready occurred.

The approach described in this specification is difficult to employ inthe locations described above using conventionally available technologybecause of the radiation fields generated by the decay of N-16 producedfrom the oxygen in the water when it flows through or near the reactorcore. The radiation field degrades the reliability of the electronicsrequired to digitize and wirelessly transmit the sensor readings. Thedifficulty is also increased by the fact that temperature of the waterflowing through the pipes exceeds the Curie point of typicalpiezoelectric materials used to produce and measure the ultrasonicradiation.

SUMMARY

This invention eliminates the foregoing concerns by using electronics,transmitters, and signal measurement devices that utilize vacuummicro-electronic device technology, allowing the critical features ofthese devices to be replaced by micro-scale vacuum tube technologyhaving performance characteristics shown to be essentially impervious toradiation damage and very high temperatures. An application of thevacuum micro-electronic devices wireless transmitter technology isdisclosed in U.S. Pat. No. 8,767,903, entitled “Wireless In-Core NeutronMonitor.”

Thus, in accordance with a broad concept of this invention, a boronconcentration monitor is provided for measuring, in real time, the boronconcentration of coolant within the piping servicing a primary loop of anuclear reactor. The boron concentration monitoring system comprises anacoustic transmitter acoustically coupled to or through the piping thatis operable to transmit an acoustic signal substantially through aninterior of the piping. An acoustic receiver is supported at a locationaround a circumference of the piping that is spaced from the acoustictransmitter, for receiving the acoustic signal from the transmitter. Acommunication mechanism is in electrical communication with the acoustictransmitter and the acoustic receiver and is configured to convey thetransmitted acoustic signal and the received acoustic signal to a remotelocation. An analyzer is in communication with the remote location andis configured to receive the received acoustic signal and thetransmitted acoustic signal from the communication mechanism and comparethe received acoustic signal and the transmitted acoustic signal andfrom the comparison determine the boron concentration within the piping.

In one embodiment of the boron concentration monitor, the analyzercompares the signal comparison to a standard to determine the boronconcentration in the piping. Preferably, the acoustic transmitter andacoustic receiver are at a known linear distance from each other and thestandard is established from an experimental determination of theattenuation of an acoustic signal in a borated water solution over theknown distance at a plurality of known boron concentrations.

In another embodiment, the communication mechanism comprises a wirelesstransmitter coupled to the acoustic transmitter and the acousticreceiver. The wireless transmitter is configured to wirelessly transmitboth the transmitted acoustic signal and the received acoustic signal tothe remote location. In the latter embodiment, the communicationsmechanism also comprises a wireless receiver configured to receive thewirelessly transmitted, transmitted acoustic signal and receivedacoustic signal at the remote location and communicate the transmittedacoustic signal and the received acoustic signal to the analyzer. In oneconfiguration of the latter embodiment the acoustic transmitter, theacoustic receiver and the wireless transmitter are powered from athermoelectric generator having a hot junction in thermal communicationwith the piping and a cold junction in thermal communication with asurrounding environment. In one arrangement of the latter embodiment thehot junction is in thermal communication with the piping through a heatpipe. Preferably, the wireless transmitter comprises two separatewireless transmitters respectively connected to the acoustic transmitterand the acoustic receiver.

In still another embodiment, the acoustic transmitter and the acousticreceiver are supported at substantially diametrically opposite positionsaround the circumference of the piping. Preferably, the acoustictransmitter and the acoustic receiver employ one or more vacuummicro-electronic devices and desirably those vacuum micro-electronicdevices are vacuum micro-electronic devices. In such an arrangement,desirably, the transmitter employs one or more vacuum micro-electronicdevices.

In another embodiment, the acoustic receiver is an ultrasonic energymeasurement sensor. In each of the foregoing embodiments, the piping maybe a charging line in fluid communication with the primary loop or a hotleg or a cold leg of the primary loop of the nuclear reactor. Each ofthe foregoing embodiments may further include a temperature sensor fordetermining the temperature of water flowing in the piping at thelocation of the acoustic transmitter and acoustic receiver thattransmits a signal representative of the temperature through thecommunication mechanism to the analyzer which determines the boronconcentration as a function of temperature. The boron concentrationmonitor may also include a pressure sensor for determining a pressure ofthe water flowing in the piping at the location of the acoustictransmitter and acoustic receiver that transmits a signal representativeof the pressure of the coolant through the communication mechanism tothe analyzer which determines the boron concentration as a function oftemperature and pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

A further understanding of the invention can be gained from thefollowing description of the preferred embodiments when read inconjunction with the accompanying drawings in which:

FIG. 1 is a simplified schematic of a nuclear reactor system to whichthis invention can be applied;

FIG. 2 is an elevational view, partially in section, of a nuclearreactor vessel and internals components to which this invention can beapplied; and

FIG. 3 is schematic of a cross-section of an exemplary reactor systempiping with the devices of one embodiment of this invention shown inblock form.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred embodiment of this invention is illustrated in FIG. 3. Thesystem comprises one or more pairs of ultrasonic transmitter 56 andultrasonic energy measurement sensors or receivers 58 coupled withwireless transmitters 60, 62 that broadcasts a signal representing theintensity of the transmitted and received ultrasonic energy. Theultrasonic transmitter 56 and receiver 58 are coupled directly to thesurface of the piping containing the fluid. The wireless signaltransmitter 60, 62 is positioned on the insulation 64 surrounding thepiping 66. The power 72 required by the ultrasonic transmitter 56 andthe wireless signal transmitter 60, 62 is generated via one or morethermo-electric generators 68 that have the heated junction connected toa heat pipe 70 that penetrates the insulation 64 surrounding the piping66 and a cold junction located on or above the outer surface of theinsulation 64 on the piping 66. Alternatively, it should be appreciatedthat the hot junction of the thermoelectric generator 68 can be directlyconnected to the piping 66. The transmitted frequency used is selectedto optimize the ability of the system to measure and detect changes inthe boron concentration. An embodiment of this system can be used totrack changes in bulk temperature corrected transmitted signal intensityand convert the changes in intensity to changes in boron concentrationrelative to a periodically manually updated reference established fromcurrent boron concentration titration measurements using existingmethods.

The system can be installed on either the reactor coolant system hot orcold leg piping or the charging line providing flow into the reactorcoolant system. An alternate embodiment would be the installation of thehardware on the pressurizer surge line piping 21. The preferredembodiment of the sensors, signal processing, and transmissionelectronics devices utilizes vacuum micro-electronic device basedelectronics and materials. Such devices, known as SSVDs, arecommercially available from Innosys Inc., Salt Lake City, Utah. Anexample of such a device can be found in U.S. Pat. No. 7,005,783. Analternate embodiment would be to use less radiation and temperaturetolerant materials and will require an increase in the requiredmaintenance cycle. Another embodiment would allow the use of powerand/or signal cables to provide transmitter power or receive transmitterand receiver output data. The measured signals are filtered to removeelectronic noise in an analyzer 74 to meet user defined accuracyrequirements using techniques well known to those skilled in the art.

An example of the parameters required to develop a correlation betweenthe boron concentration in the reactor coolant system and theattenuation of the transmitted acoustic or ultrasonic energy iscontained in an article entitled “Modeling of Acoustic Wave Absorptionin Ocean” by T. B. Mohite-Patil, et al. International Journal ofComputer Applications, November 2010:

Absorption coefficient due to Boric Acid

$\begin{matrix}{{attn}_{1} = \frac{A_{1}P_{1}f_{1}f^{2}}{f_{1}^{2} + f^{2}}} & \; \\{{A_{1} = {\frac{8.86}{c} \times 10^{({{0.78\mspace{11mu} {pH}} - S})}}},} & {{dB}\mspace{11mu} {Km}^{- 1}{KHz}^{- 1}} \\{{P_{1} = 1},} & \; \\{{f_{1} = {2.8\left( {S/35} \right)^{0.5} \times 10^{({4 - {1245/\theta}})}}},} & {KHz}\end{matrix}$

Where c is the sound speed (m/s), given by

c=1412+3.21T+1.19 S+0.0167 D,

T is the temperature(°C.),

θ=273+T,

S is the salinity(‰), and D is the depth (m).

The boron concentration in the liquid is obtained by solving therelationship for pH of the liquid and converting the pH information toboron concentration using the known properties of boron in an aqueoussolution. Temperature and Pressure (Depth) information can be determinedfrom existing sensors. Salinity (S) is determined based on known waterproperties. The frequency used is selected to optimize the ability tomeasure and detect changes in the boron concentration. Thus, the boronconcentration can be determined by comparing the attenuation of thetransmitted signal over a known travel path through the coolant with astandard obtained by transmitting a like acoustic signal over the knowntravel path through a plurality of different boron concentrations inwater solutions with the concentrations determined by conventionalchemical analysis. Alternatively, with the pressure and temperature ofthe coolant known a real-time reading of the boron concentration can behad from a computer mathematical analysis from the foregoingmathematical correlation.

While specific embodiments of the invention have been described indetail, it will be appreciated by those skilled in the art that variousmodifications and alternatives to those details could be developed inlight of the overall teachings of the disclosure. Accordingly, theparticular embodiments disclosed are meant to be illustrative only andnot limiting as to the scope of the invention which is to be given thefull breadth of the appended claims and any and all equivalents thereof

What is claimed is:
 1. A boron concentration monitor for measuring, inreal time, the boron concentration of coolant within a piping servicinga primary loop of a nuclear reactor comprising: an acoustic transmitteracoustically coupled to or through the piping operable to transmit anacoustic signal substantially through an interior of the piping; anacoustic receiver supported at a location around a circumference of thepiping that is spaced from the acoustic transmitter, for receiving theacoustic signal; a communication mechanism in electrical communicationwith the acoustic transmitter and the acoustic receiver and configuredto convey the transmitted acoustic signal and the received acousticsignal to a remote location; and an analyzer is structured to be incommunication with the remote location and is configured to receive thereceived acoustic signal and the transmitted acoustic signal from thecommunication mechanism and compare the received acoustic signal and thetransmitted acoustic signal and from the comparison determine the boronconcentration within the piping.
 2. The boron concentration monitor ofclaim 1 wherein the analyzer compares the signal comparison to astandard to determine the boron concentration in the piping.
 3. Theboron concentration monitor of claim 2 wherein the acoustic transmitterand acoustic receiver are at a known linear distance from each other andthe standard is established from an experimental determination of theattenuation of an acoustic signal in a borated water solution over theknown distance at a plurality of known boron concentrations.
 4. Theboron concentration monitor of claim 1 wherein the communicationmechanism comprises: a wireless transmitter coupled to the acoustictransmitter and the acoustic receiver and configured to wirelesslytransmit both the transmitted acoustic signal and the received acousticsignal to the remote location; and a wireless receiver configured toreceive the wirelessly transmitted acoustic signal and received acousticsignal and communicate the transmitted acoustic signal and the receivedacoustic signal to the analyzer at the remote location.
 5. The boronconcentration monitor of claim 4 wherein the acoustic transmitter, theacoustic receiver and the wireless transmitter are powered from athermoelectric generator having a hot junction in thermal communicationwith the piping and a cold junction in thermal communication with asurrounding environment.
 6. The boron concentration monitor of claim 5wherein the hot junction is in thermal communication with the pipingthrough a heat pipe.
 7. The boron concentration monitor of claim 4wherein the wireless transmitter comprises two separate wirelesstransmitters respectively connected to the acoustic transmitter and theacoustic receiver.
 8. The boron concentration monitor of claim 1 whereinthe acoustic transmitter and the acoustic receiver are supported atsubstantially diametrically opposite positions around the circumferenceof the piping.
 9. The boron concentration monitor of claim 1 wherein theacoustic transmitter and the acoustic receiver employ one or more vacuummicro-electronic devices.
 10. The boron concentration monitor of claim 9wherein the solid state vacuum device is a vacuum micro-electronicdevice.
 11. The boron concentration monitor of claim 4 wherein thewireless transmitter employs one or more vacuum micro-electronicdevices.
 12. The boron concentration monitor of claim 11 wherein thesolid state vacuum device is a vacuum micro-electronic device.
 13. Theboron concentration monitor of claim 1 wherein the acoustic receiver isan ultrasonic energy measurement sensor.
 14. The boron concentrationmonitor of claim 1 wherein the piping is a charging line in fluidcommunication with the primary loop.
 15. The boron concentration monitorof claim 1 wherein the piping is a hot leg or a cold leg of the primaryloop of the nuclear reactor.
 16. The boron concentration monitor ofclaim 1 including a temperature sensor for determining a temperature ofwater flowing in the piping at the location of the acoustic transmitterand acoustic receiver and transmitting a signal representative of thetemperature through the communication mechanism to the analyzer whichdetermines the boron concentration as a function of temperature.
 17. Theboron concentration monitor of claim 14 including a pressure sensor fordetermining a pressure of the water flowing in the piping at thelocation of the acoustic transmitter and acoustic receiver andtransmitting a signal representative of the pressure through thecommunication mechanism to the analyzer which determines the boronconcentration as a function of temperature and pressure.
 18. A method ofmonitoring a boron concentration of a borated water solution inreal-time, comprising the steps of: transmitting an acoustic signalthrough the borated water solution; receiving the transmitted acousticsignal after the transmitted acoustic signal has passed through at leasta portion of the borated water solution, at a known distance between atransmitter structured to transmit the acoustic signal and a receiverconfigured to receive the transmitted acoustic signal; comparing thereceived acoustic signal to the transmitted acoustic signal to determinean attenuation of the transmitted acoustic signal through the boratedwater solution; and determining the boron concentration from theattenuation of the transmitted signal.
 19. The method of claim 18wherein the determining step compares the attenuation with a standardobtained by chemically analyzing a plurality of different concentrationsof boron in borated water solutions and measuring the attenuation overthe known distance in each of the plurality of different concentrationsof boron.
 20. The method of claim 18 wherein the determining stepcomprises: obtaining the pressure and temperature of the coolant at atime of transmission of the acoustic signal; and using the attenuation,the temperature and the pressure to mathematically determine the boronconcentration in real-time.